The present invention relates to a method of forming a semiconductor device, and more particularly to a method of dry etching a silicon layer to make a groove.
It is a well-known etching method to etch a polysilicon layer by using a resist as a mask. Recently, it has become a requirement to complete the etching more quickly. The polysilicon layer is therefore etched using the resist as a mask by using an etching gas which has low selectivity against the resist to remove the polysilicon quickly as a first etching step before the resist is completely removed from polysilicon. As such, a resist is etched at the same time as the polysilicon. Then, as a second step, the polysilicon is etched with using the remaining resist as a mask by using an etching gas which has high selectivity against the resist. As such in the second step, the polysilicon is etched almost without etching the resist. Thus etching is achieved by the two step process etching. However, during the first etching step, the etching of the resist results in particulate etched resist which is re-deposited (settles) on the surface of the polysilicon. Therefore a problem occurs in that the polysilicon is not properly etched to the desired shape because of the re-deposited resist found on the polysilicon as a result of the first etching step just prior to the second etching step, acting as a mask to the second etching step.